The present invention relates generally to linear translation systems and laser imaging systems incorporating such systems. In particular, the present invention relates to a linear translation system for use in an internal drum type optical scanner assembly suitable for use in a medical imaging system.
Laser imaging systems are commonly used to produce photographic images from digital image data generated by magnetic resonance (MR), computed tomography (CT) or other types of scanners. Systems of this type typically include a continuous tone laser imager for exposing the image on photosensitive film, a film processor for developing the film, and an image management subsystem for coordinating the operation of the laser imager and the film processor.
The digital image data is a sequence of digital image values representative of the scanned image. Image processing electronics within the image management subsystem processes the image data values to generate a sequence of digital laser drive values (i.e., exposure values), which are input to a laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film in a raster pattern for exposing the image on the film.
The continuous-tone images used in the medical imaging field have very stringent image-quality requirements. A laser imager printing onto transparency film exposes an image in a raster format, the line spacing of which must be controlled to better than one micrometer. In addition, the image must be uniformly exposed such that the observer cannot notice any artifacts. In the case of medical imaging, the observers are professional image analysts (e.g., radiologists).
Film exposure systems are used to provide exposure of the image on photosensitive film. Known film exposure systems include a linear translation system and a laser or optical scanning system. The laser scanning system includes a laser scanner with unique optical configurations (i.e., lenses and mirrors), for exposure of the image onto the film.
The linear translation system provides for movement of the laser scanning system in a direction perpendicular to the scanning direction, such that a full image may be scanned on a piece of photosensitive film. Linear translation systems are found in products such as plotters, printers, flatbed scanners, and internal drum laser scanners.
Traditional linear translation systems include three main components, a stationary member, a moving member (e.g., a carriage), and a drive mechanism. In a linear translation system where rigidity, positional accuracy, and high load carrying capacity are required, lead screw mechanisms are preferred as the drive mechanism. Belts and cable systems are used in systems characterized by flexibility, light loads, and low costs, such as plotters and ink jet printers.
Known linear translation systems are usually designed for positional repeatability. Although such systems work well for positional repeatability type scanning operations, such linear translation systems were not designed to minimize velocity variation which is critical to a "continuous" scan system or a continuous "step-scan" system wherein the linear translation system moves or steps the laser scanning system as the laser scanning system scans a scan line across the photosensitive film. In continuous laser scanning applications, velocity variations cause the scan lines to be unevenly spaced and result in a variety of image artifacts on the photosensitive film.